The invention relates to a securing system in particular for motor vehicles.
Chip card systems for a keyless entry are already known in which e.g. the doors and the trunk of the respective motor vehicle can be opened and its engine started by means of a customer identification device (CID), such as for example a chip card, which replaces the key and which serves as user identification. In this, transmission and response signals are exchanged between at least one transmitter which is integrated into the vehicle and the CID. Before a respective function can be carried out the identification code which is transferred from the CID is checked. In this it is sufficient for a user carrying a valid CID on his person to be near the vehicle. A system of this kind for a keyless entry is typically a bidirectional HF communication system, in which for example a frequency of 125 kHz is used for a signal transmission from the motor vehicle to the CID and for example a frequency of 433 MHz is used for a signal transmission from the CID to the motor vehicle.
In these known systems the following two problems mainly arise: (1) It must be distinguished whether the CID is located outside or inside the vehicle. This is currently achieved by the use of a plurality of 125 kHz antennas, which is very cost-intensive and brings about the danger of instabilities in view of the antenna tolerances. (2) The so-called relay station problem, which consists in it being possible for the vehicle to be opened by a thief in that the latter bridges the connection to the CID, which is far remote from the vehicle, via one or more relay stations, can not be avoided with a system operating at 433 MHz or 125 kHz.
In vehicles with keyless entry the inner/outer localization of the CID takes place up to now via a large number of HF coils, which is relatively cost-intensive. The interior space protection and at least parts of the keyless entry have up to now been realized through separate sensors.
The object of the invention is to create a more reliable and more economical securing system in which the above named disadvantages are elininated.
For satisfying this object the securing system in accordance with the invention comprises at least one multi-functional sensor, which is simultaneously provided both as a radar unit and as a transmitter/receiver unit for communicating with an external device.
As a result of this execution it is for example possible to simultaneously fulfill with one and the same sensor device both radar-typical functions, such as for example distance measurements and/or localization functions, and the functions which are typical of the systems for a keyless entry. As a whole there results an extremely simple and correspondingly economical construction. With the simpler construction the reliability is also correspondingly increased.
The multi-functional sensor preferably comprises a short distance radar (SDR) sensor for an interior space protection which operates in the high frequency range. In accordance with the invention a radar sensor of this kind can in particular also be provided simultaneously as a transmitter/receiver unit for communicating with the external device.
In particular in regard to as ideal an area monitoring and/or object localization as possible it is expedient when the multi-functional sensor comprises a plurality of receivers and/or a plurality of transmitters.
In an expedient practical embodiment of the securing system in accordance with the invention the multi-functional sensor comprises at least one transmitter and/or at least one receiver for a wireless communication with the external device.
The external device can in particular be a customer identification device (CID) which serves as user identification and which is preferably realized through an active receiver/transmitter unit or as a transponder.
It is also advantageous when the multi-functional sensor comprises at least two transmitters and/or at least two receivers for localizing the external device. By means of a multi-functional sensor of this kind it can then in particular also be determined whether the external device is located inside or outside the monitored interior space. In this the signals which are received by different receivers and/or are originating from different transmitters are preferably compared with one another for localizing the external device. Via a signal comparison of this kind it can then for example be determined whether the relevant external device is provided inside or outside the monitored interior space.
In an expedient practical embodiment the respective distance between the multi-functional sensor and the external device can be determined through measuring the travel time of the signals which are exchanged between the multi-functional sensor and the external device. It is thereby for example possible to detect a possible unauthorized use by means of a so-called relay station (relay station attack). On the basis of the respective determined distance between the sensor and the external unit, which is for example formed by a CID, the relevant evaluation unit can reliably appraise the respective situation in order to prevent where required the respective functions from being carried out and/or an alarm from being triggered.
A preferred practical embodiment of the securing system in accordance with the invention is distinguished in that the external device picks up signals which are originating from the multi-functional sensor, and which are preferably HF-modulated signals, modifies them in a defined way and then emits them again. The travel time measurement preferably takes place on the basis of such signals which are modified in a defined way by the external device and are picked up again by the multi-functional sensor.
Thus for example a short distance radar (SDR) sensor can at the same time be used for realizing the functions of a system for a keyless entry. Thus for example 24 GHz transceivers of the short distance radar sensor can be used at the same time for communicating with the external device, such as for example a device serving for user identification (CID). With a conception of this kind it is moreover possible to eliminate the two prime priority problems of the previous system for a keyless entry system. Thus an attempted unauthorized use by means of a relay station (relay station attack) can now be detected for example through a corresponding distance measurement and/or through the determination of whether the external device which is formed for example by a CID is located inside or outside the monitored interior space. A single radar sensor unit is sufficient for this.